In a gas turbine engine, ambient air is drawn into a compressor section. Alternate rows of stationary and rotating aerofoil blades are arranged around a common axis, together these accelerate and compress the incoming air. A rotating shaft drives the rotating blades. Compressed air is delivered to a combustor section where it is mixed with fuel and ignited. Ignition causes rapid expansion of the fuel/air mix which is directed in part to propel a body carrying the engine and in another part to drive rotation of a series of turbines arranged downstream of the combustor. The turbines share rotor shafts in common with the rotating blades of the compressor and work, through the shaft, to drive rotation of the compressor blades.
It is well known that the operating efficiency of a gas turbine engine is improved by increasing the operating temperature. The ability to optimise efficiency through increased temperatures is restricted by changes in behaviour of materials used in the engine components at elevated temperatures which, amongst other things, can impact upon the mechanical strength of the components. This problem is addressed by providing a flow of coolant about these components. It is known to take off a portion of the air output from the compressor (which is not subjected to ignition in the combustor and so is relatively cooler) and feed this to surfaces of components downstream which are likely to suffer damage from excessive heat.
Within the combustor section rapidly flowing air is directed towards the fuel spray nozzle. Sprayed fuel and the air are mixed and delivered to a combustion chamber where the mixture is ignited. A heat shield is arranged around the nozzle exit and the front of the combustion chamber to further assist in protecting the combustor components from heat damage. The fuel spray and hot gases exiting the nozzle (prior to ignition) provides an additional cooling effect between the nozzle exit and the combustion chamber. In known combustor arrangements, flow onto the cooler side of the heat shield is metered by a meter panel. Typically the meter panel consists of a metal sheet perforated with 100′s of drilled holes.
Fuel injection components and components of the combustion chamber are typically coupled by floating seals which allow relative movement between the components which can occur due to differential expansion of components at elevated temperatures. With improvements in fuel delivery and fuel/air mixing, higher burn temperatures have been achieved and consequently, improved cooling systems are needed to maintain mechanical integrity of the fuel delivery and combustor components. Furthermore, floating seals are susceptible to corrosion and wear as a consequence of the increased temperatures and consequently become less effective and less reliable.